作者:Keigo Kamata、Tomohisa Hirano、Ryo Ishimoto、Noritaka Mizuno
DOI:10.1039/c002318c
日期:——
The selenium-containing dinuclear peroxotungstate, [(n-C4H9)4N]2[SeO4WO(O2)2}2] (I), acts as a homogeneous catalyst for the selective oxidation of various kinds of cyclic mono- and disulfides with 30% aqueous H2O2. The cyclic disulfides were selectively oxidized to the corresponding monosulfoxides with one equivalent of H2O2 with respect to the sulfides. In the presence of two equivalents of H2O2, the oxidation of dibenzothiophene gave the corresponding sulfone in 98% yield under the mild conditions. The negative Hammett Ï value (â0.62) for the competitive oxidation of p-substituted thioanisoles and the low XSO (XSO = (nucleophilic oxidation)/(total oxidation)) value of 0.14 for the I-catalyzed oxidation of thianthrene 5-oxide (SSO) revealed that I is a strong electrophilic oxidant. The reactivities of the di- and tetranuclear peroxotungstates with XO4nâ ligands (X = Se(VI), As(V), P(V), S(VI), and Si(IV)) were strongly dependent on the kinds of hetero atoms. The reaction rates for the sulfoxidation decreased with an increase in the XSO values and a peroxotungstate with a stronger electrophilicity was more active for the sulfoxidation. The kinetic and mechanistic investigations showed that the electrophilic attack of the peroxo oxygen at the sulfur atom is a key step in the sulfoxidation. The computational investigation supported the high chemoselectivitiy for the sulfoxidation of diallyl sulfide.
含硒双核过钨酸盐[(n-C4H9)4N]2[SeO4WO(O2)2}2](I)作为均相催化剂,可用于30%水溶液H2O2对各种环状单硫醚和二硫醚的选择性氧化。环状二硫醚被H2O2选择性氧化为相应的单亚砜,H2O2与硫醚的摩尔比为1:1。在H2O2与硫醚摩尔比为2:1的情况下,二苯并噻吩在温和条件下被氧化为相应的砜,产率达98%。对于竞争氧化具有对位取代基的硫醚,负Hammett Ï值(-0.62)以及在I催化氧化噻蒽5-氧化物(SSO)过程中XSO(XSO =(亲核氧化)/(总氧化))值为0.14,表明I是一种强亲电氧化剂。具有XO4n-配体的双核和四核过钨酸盐(X = Se(VI)、As(V)、P(V)、S(VI)和Si(IV))的反应活性强烈依赖于杂原子的种类。磺氧化反应速率随着XSO值的增加而降低,亲电性更强的过钨酸盐在磺氧化反应中表现出更高的活性。动力学和机理研究表明,过氧氧对硫原子的亲电攻击是磺氧化反应的关键步骤。计算研究表明,烯丙基硫醚的磺氧化反应具有高化学选择性。